This invention relates to reactor arrangements having means for mixing reactants and to the heating of reactants in such reaction zones.
There are many homogenous or heterogeneous chemical reactions involving liquid and/or gas vapor phases that benefit from the intimate mixing of the reactants in the reaction zone.
This intimate mixing is usually supplied by a tubular reactor. These reactors consist of a long conduit into which the reactants are injected. Mixing of the reactants occurs as they flow down the conduit. The design requirements for these reactors include the variables of temperature, degree of mixing and residence time. Direct or indirect heat transfer may be employed to control temperature conditions within the tubular reactor. For example it is known that such reactors may be externally jacketed to circulate a heat exchange medium on the outside surface of an extended reaction conduit and thereby provide indirect heating or cooling over the entire external surface of the reactor.
The primary variables influencing the design of the mixing reactors are the degree of mixing, the residence time, and the temperature of the reaction. The length of the conduit or pipe is usually sized to control residence time. The degree of mixing is largely a function of the flow regime within the conduit. In open tubular reactors the diameter largely controls the flow regime therein. Thus optimal velocity for tubular reactions is established when the pipe diameter correctly keeps the flow in the desired flow regime within a pipe or conduit having a length that provides the proper residence time for the reaction. The temperature depends on the heat of reaction and the degree to which heat may be added or withdrawn via intermediate injection of reactants or diluents and the availability of indirect heat exchange.
External heating and the addition of fluids do not always offer satisfactory temperature control. Since many mixing reactors depend on high fluid velocities through the reaction zone, processes with high heats of reaction may not receive enough heat flux to maintain optimum temperatures without exceeding local temperature limitations for the reactants. The direct addition of heating or cooling fluids may also interfere with process control by varying the velocity and residence time through the reaction zone as well as composition concentrations.
The requirements for mixing and residence time are also not always fully compatible, and therefore, the diameter of the conduit containing a mixing reactor may represent a compromise in optimum values to control mixing and residence time. In addition, many tubular reactors require very long pipe lengths at high velocities to achieve the necessary mixing. One means of overcoming the incompatibility in the flow regime or residence time and long length requirements is the use of internal mixers within a tubular reactor or other reaction zone. Internal mixing devices include stirred reactors and static mixers.
In some cases, conduit or tubes of mixing reactors are also unable to provide the intensity of the mixing that may be important for certain reactions. In order to overcome mass transfer limitations, many reactions that require intimate mixing of reactants also require the mixing be accomplished with a high degree of shear forces between the fluids. The high shear forces create the necessary phase dispersion to overcome mass transfer limitations inherent in the fluids and to provide the contacting necessary for precise reaction control.
Stirred tank reactors in many cases may provide the necessary shear forces to eliminate mass transfer limitations. However, stirred tank reactors often provide unwanted areas of stagnation that allow variations in residence time and degrade the products obtained from certain reactions. In addition, the mechanical elements of stirred tank reactors may prove troublesome. When operating at high pressure, impeller shaft seal leakage is particularly difficult to prevent.
Static mixers are commonly used to supply additional mixing energy to the reactor instead of mechanical stirred reactors. These types of static mixers include simple static mixers, fluidic mixers and vortex mixers. Simple static mixers are effective in forming and dispersing gas bubbles in a statistical distribution.
U.S. Pat. No. 5,409,672 issued to Centinkaya shows a static mixer arrangement provides a high fluid shearing while minimizing pressure drop.
U.S. Pat. No. 5,538,700 issued to Koves shows an arrangement of corrugated plates that use a perforated insert plate to introduce additional turbulence into heat exchange channels.
U.S. Pat. No. 5,525,311 issued to Girod et. al. show a process and arrangement that uses plates to defined a plurality of catalyst retaining channels for processing a reactant stream interleaved with a plurality of channels that receive a heat exchange fluid.
It is an object of this invention to provide a mixing type reactor that can provide intimate mixing and efficient internal heat exchange.
It is a further object of this invention to provide a mixing type reactor that can provide intimate mixing and simultaneous internal heat exchange with a desired degree of fluid shearing.
This invention is a mixing reactor that passes a flowing stream of reactants through a plurality of mixing devices that simultaneously provide indirect heat exchange of the reactants. The mixing devices provide intimate mixing by passing the reactants through a plurality of narrow channels defined by parallel plate elements that channel a heat exchange fluid on their opposite side to provide the simultaneous indirect heat exchange. The heat channels can have any desired degree of mixing intensity by providing irregularities in the channel walls or a flow path that supplies the desired degree of fluid shear. Preferably the mixing reactor provides a series of mixing devices with heat exchange along the length of the conduit flow path with space between the devices for remixing of the fluid reactants. Thus, the degree of stirring required by the reaction can be intensified by the addition of the required number of mixing devices positioned along the flow path through the tube or conduit of the reactor. The additional stages of mixing or shear may be added to continue mixing components as reactants are produced or to maintain dispersion as additional reagents or catalysts are added between stages of mixing or as intermediate fluids are withdrawn from the reactor.
Accordingly, in one embodiment this invention is an apparatus for the plug flow reaction of one or more reactants in the presence of gas, liquid or mixed phase fluids. The apparatus includes a containment conduit having an inlet and an outlet end for passing fluid from the inlet end to the outlet end and establishing a flow direction through the conduit. At least two spaced apart mixing sections comprising a plurality of spaced apart plates definine heat exchange flow channels and reactant flow channels, the plates retain turbulence inducing structures that extend transversely across the reactant flow channels and the plates define reactant channel inlets for the reactant channels at the upstream end of the mixing sections and define reactant channel outlets for the reactant channels at the end of the mixing section opposite the reactant channel inlets. A distribution manifold for distributes a heat exchange fluid to the sides of the heat exchange channels. A collection manifold for collects a heat exchange fluid from the sides of the heat exchange channels.
In a more specific embodiment this invention comprises an apparatus for the plug flow reaction of one or more reactants in the presence of a gas, a liquid or mixed phase fluids. The apparatus includes at least three chamber conduit sections defining connecting volumes for passing a reactant stream from a contactor inlet, through at least two mixing devices and out of the contactor outlet and establishing a reactant flow path. A plurality of parallel plates, spaced apart in a stacked arrangement, form a plurality of reactant flow channels interleaved with a plurality of heat exchange channels in each mixing device and provide each mixing device with a rectilinear profile transverse to the reactant flow path. The plates retain turbulence inducing structures that extend transversely into the reactant flow channels. The plates define reactant channel inlets for the reactant channels at the upstream end of the mixing device and reactant channel outlets for the reactant channels at the end of the mixing device opposite the reactant channel inlets. The plates define a heat exchange inlet on one side of the heat exchange channels and a heat exchange outlet on the opposite side of the heat exchange channels. A first curved containment section having a concave side defines a distribution manifold over the heat exchange inlet side of each mixing device for distributing a heat exchange fluid to the sides of the heat exchange channels. A second curved containment section having a concave side defining a collection manifold over the heat exchange outlet side of each mixing device collects a heat exchange fluid from the sides of the heat exchange channels.
Additional objects, embodiments and details of this invention are disclosed in the following detailed description of the invention.